1. Field of the Invention
The present invention relates to a pressure-sensitive copying paper and, more particularly, it relates to a pressure-sensitive copying paper wherein a novel color former is used.
2. Description of the Prior Art
In general, pressure-sensitive copying papers utilizing the color reaction between substantially colorless organic compound (hereinafter referred to as a color former) such as Malachite Green lactone, benzoyl leucomethylene blue, Crystal Violet lactone, Rhodamine B lactam, 3-substituted amino-7-substituted aminofluoran, 3-methyl-2,2-spirobi(benzo[f]chromene) or the mixture thereof and an adsorptive or reactive compound capable of developing color when brought into contact with the color former (hereinafter referred to as a color developer) such as a clay mineral (e.g., acid clay, activated clay, attapulgite, zeolite, bentonite, kaolin, etc.), an organic acid (e.g., succinic acid, tannic acid, gallic acid, phenolic compound, etc.) or an acidic polymer (e.g., phenolformaldehyde resin, etc.) as well known (e.g., as disclosed in U.S. Pat. Nos. 2,505,470, 2,505,471, 2,505,489, 2,548,366, 2,712,507, 2,730,456, 2,730,457, 3,418,250, 3,501,331, 3,669,711, 3,427,180, 3,455,721, 3,516,845, 3,634,121, 3,672,935, and 3,732,120).
In the present invention, the color former and the color developer are defined as follows from the viewpoint of electronic theory. That is, the color former is a substance capable of being colored when donating electrons or accepting protons, whereas the color developer is a substance which accepts electrons or donates protons.
A color former of a pressure-sensitive copying paper must possess a rapid coloring rate and show high color density, and the colored dye must possess a desired hue and be excellent in light resistance and heat resistance. As a color former which is colored blue to green, Malachite Green lactone (3,3-bis(p-dimethylaminophenyl)phthalide) is heretofore known. However, this color former has the defect that, since its lactone ring is not opened even when brought into contact with a color developer, the coloring rate thereof is slow and the color density is low. Thus, improvement in the color former has been desired.
It is, therefore, an object of the present invention to provide a pressure-sensitive copying paper which is capable of forming a colored image having a high color density with a rapid coloring rate.
Another object of the present invention is to provide a pressure-sensitive copying paper which is capable of forming a color image excellent in light resistance and heat resistance.
A further object of the present invention is to provide a pressure-sensitive copying paper which is capable of being colored blue to green.
Still a further object of the present invention is to provide a pressure-sensitive copying paper which is capable of being colored various hues.
Also an object of this invention is to provide a 1,3-dihydro-(1-oxo or 3-oxo)-benzo[b]thieno[2,3-C]furan derivative, useful as a color former.